Mapping Cell Types and Efferent Pathways in the Ascending Relaxin-3 System of the Nucleus Incertus

Area of Science:

• Neuroscience
• Molecular Biology
• Genetics

Background:

• Relaxin-3 (Rln3) is a peptide neurotransmitter found in specific brain regions.
• Understanding the precise localization and connectivity of Rln3-expressing neurons is crucial for deciphering its role in neural circuits.

Purpose of the Study:

• To generate and characterize a transgenic mouse line for studying Rln3-expressing neurons.
• To map the molecular identity and axonal projections of Rln3 neurons in the brain.
• To investigate the synaptic connections of Rln3 neurons.

Main Methods:

• Generation of Rln3 transgenic mice using targeted recombination.
• In situ hybridization to confirm Rln3 mRNA expression.
• Adeno-associated virus (AAV)-mediated anterograde tracing.
• Rabies virus (RV)-mediated transsynaptic retrograde tracing.

Main Results:

• Rln3 expression was confirmed in nucleus incertus (NI), deep mesencephalon (DpMe), and periaqueductal gray (PAG).
• NI-Rln3 neurons project extensively to the limbic cortex, septum, hippocampus, and hypothalamus.
• DpMe and PAG Rln3 neurons have more localized projections.
• Rln3 neurons in the NI are GABAergic and likely synapse with septal GABAergic neurons.

Conclusions:

• The study successfully generated a tool for Rln3 neuron research.
• NI-Rln3 neurons form a significant ascending pathway influencing forebrain circuits.
• These findings provide a detailed map of Rln3 neuron connectivity, essential for future functional studies.